This project is designed to investigate the roles of monocytes in limiting blood-borne metastasis of tumor cells, and to provide a valid basis for effective immunochemotherapy (or prophylaxis) of metastatic spreading. Utilizing both metastasizing and nonmetastasizing syngeneic tumor lines of DBA/2J mice, host immunity is semi-quantitatively assessed in normal and tumor-bearing animals by injection of radio-labeled tumor cells and by measuring the rate of tumor cell destruction in various target organs of these animals, and the results are evaluated in relation to eventual tumor outgrowth in each organ. Responses of tumors to chemotherapy and the metastasizing ability of tumor cells are also comparatively investigated. Suppression by commonly employed chemo- and/or radiotherapeutic regimens of host defense functions and their possible restoration or augmentation by monocytic effectors are studied. Possible roles of T lymphocytes in such monocyte functions, as well as roles of monokines in activation of T cell activities, are investigated.